For example, a heat treatment apparatus for applying heat treatment to a metallic component (workpiece), etc., is known (for example, refer to Patent Application Document 1). A quenching device as a heat treatment apparatus described in Patent Application Document 1 is configured to apply quenching treatment (rapid cooling) to a heated workpiece. In the rapid cooling treatment, the workpiece is disposed within a portion extending vertically in a duct. Then, by a coolant passing through this duct, the workpiece is cooled.